Planetary roller screw spindles (also referred to as planetary roller screw drives) have for many years formed part of the prior art and are described, for example, in DD 0277308 A5. The publication DE 10 2010 047 800 A1, for example, discloses a planetary roller screw drive which is contained in a hydrostatic actuator in the form of a hydrostatic clutch actuator, in order to convert a rotational movement generated by an electric motor into an axial movement.
The publication DE 10 2010 011 820 A1 discloses a planetary roller screw drive, having a screw spindle and a nut arranged on the screw spindle, and having a plurality of planets, which are distributed over the circumference and arranged between the screw spindle and the nut, and which are arranged so that they can roll on the inner circumference of the nut and on the outer circumference of the screw spindle. In this solution the planets are provided with a pre-tensioning device, wherein the nut comprises two nut parts axially moveable relative to one another, and wherein the pre-tensioning device comprises a spring element sprung against one of the nut parts. The nut performs two functions, being both a drive component and part of the pre-tensioning device.
Hydraulic operating actuators are known which actuate a clutch by way of a hydraulic actuating line. These differentiate between a pressure chamber and a fluid reservoir, which are connected to one another via a venting hole. Running over the venting hole towards the pressure chamber seals the pressure chamber off from the fluid reservoir, and volume equalization can no longer take place. Here, according to DE 10 2013 204 561 A1 three seals are arranged for sealing off the pressure chamber. Two of the three seals are arranged axially in series. Of these, upon actuation a first seal seals off the pressure chamber from the venting hole and the other, second seal seals the electric motor chamber off from the fluid reservoir. The second seal here is particularly critical with regard to leakage losses, because it serves for sealing off from the atmosphere.
Flooding the inner chamber with coolant and/or lubricant is also known in the case of freewheel clutches (DE 10 2012 221 136 A1).
DE 40 36 209 C1 describes a planetary gear wherein the gear interior is partially filled with lubricating oil and is sealed off from the outside.
In an as yet unpublished document a flooded actuator is described, wherein the fluid chamber and the housing interior form one common volume. Under a relative movement between the spindle and the planetary rollers, however, only a minimal exchange of fluid occurs between the interior of the planetary roller screw drive defined by the sleeve and the remainder of the housing interior.
One disadvantage is the sealing necessary in the case of grease-lubricated planetary roller screw drives, and the space needed for the grease, the grease being subject to ageing. Furthermore, there is no heat energy transfer through the lubricants, making it impossible to cool the planetary roller screw drives. All in all these factors can have a negative influence on the efficiency of the actuator.